The phrase blends the familiar what are those reaction format with kowai, the Japanese word for scary, which helps explain its appeal in anime and horror meme circles. Online, creators reuse short confused voice lines like this because they work without context and can be layered over almost any unsettling sound. It has found a niche in edits where a mundane noise is treated as terrifying, from creaky floors to distant game audio, letting the overreaction carry the joke rather than the noise itself.